This invention relates to a modulator for modulating a beam of light having selectively thermally deformable members for providing a diffraction grating.
Electro-mechanical spatial light modulators are used in a variety of applications, including image processing, display, optical computing and printing, and wavelength division multiplexing and spectrometers. Electro-mechanical gratings are well known in the patent literature, see U.S. Pat. No. 4,011,009, xe2x80x9cReflection diffraction grating having a controllable blaze angle,xe2x80x9d issued on Mar. 8, 1977 to W. L. Lama et al and U.S. Pat. No. 5,115,344, xe2x80x9cTunable diffraction grating,xe2x80x9d issued on May 19, 1992 to J. E. Jaskie. More recently, Bloom et al described an apparatus and method of fabrication for a device for optical beam modulation, known to one skilled in the art as a grating-light valve (GLV), see U.S. Pat. No. 5,311,360, xe2x80x9cMethod and apparatus for modulating a light beam,xe2x80x9d issued on May 10, 1994. According to the prior art, for operation of the GLV device, an attractive electrostatic force is produced by a single polarity voltage difference between the ground plane and the conducting layer atop a plurality of deformable members called ribbons. This attractive force changes the heights of the ribbons relative to the substrate. By modulating the voltage waveform, it is possible to modulate the diffracted optical beam as needed by the specific application.
One problem with the prior art light modulators is that they use an electrostatic activation force that is nonlinear. Specifically, as the voltage applied to the modulator increases from zero, the activated deformable members (ribbons) deflect incrementally until they reach approximately ⅓ of their full scale deflection, and then they jump the remaining distance until they impact the substrate. Because of this limited range of motion, such modulators are typically designed to efficiently diffract a single wavelength of light. Moreover, they have a relatively high activation voltage, and encounter stiction problems when the deformable members contact the substrate. Therefore, a need exists for a modulator that can efficiently diffract a range of wavelengths, that can operate at relatively low voltages, and that can operate without the deformable members contacting the substrate to eliminate stiction.
It is an object of the present invention to provide a modulator for modulating an incident beam of light by providing more versatile deformable members.
The object is achieved in a modulator for modulating an incident beam of light, comprising:
a structure defining a cavity and having a base and side walls surrounding the base;
a first plurality of equally spaced apart thermally deformable reflective members having opposing end edges integrally formed in the side walls of the structure above the cavity, wherein each one of the plurality of thermally deformable members includes at least a top layer and a bottom layer, wherein the top layer is conductive, and has a higher coefficient of thermal expansion than the bottom layer, and wherein the top layer has end sections adjacent to the support walls and a midsection, with the end sections having a higher resistance than the midsection;
a second plurality of equally spaced apart, electrically isolated fixed members having opposing end edges integrally formed in the side walls of the structure just above the cavity, wherein each one of the second plurality of fixed members has a reflective top surface for reflecting the incident beam of light, and wherein each fixed member of the second plurality of fixed members is arranged between adjacent spaced apart deformable members of the plurality of thermally deformable members such that the deformable members and the fixed members form a substantially planar light reflection surface; and
means for applying current through the top layers of the first plurality of equally spaced apart thermally deformable reflective members that causes them to deflect into the cavity and away from the substantially planar light reflection surface, whereby light reflecting from the first plurality of thermally deformable reflective members destructively interferes with light reflected from the second plurality of fixed members thereby causing modulation of the incident light.
An advantage of the light modulator of the invention is it can efficiently diffract a range of wavelengths because its thermally deformable members can be deformed over the full range of their motion. A further advantage is that it can operate at lower voltages than competitive electrostatically activated light modulators. An additional advantage of the invention is that the thermally deformable members do not contact any surfaces during their motion thereby eliminating the problem of stiction.